1. Field of the Invention
This invention relates generally to a washing machine; more particularly, to drive control of the motor in such a washing machine.
2. Description of the Prior Art
In washing machines, a rotatable tub serving both as a wash tub and as a dehydration basket is rotatably provided in an outer tub, as is well known in the art. An agitator is rotatably mounted on the bottom of the rotatable tub. The rotatable tub and the agitator are rotated by an electric motor. When a wash operation is executed, a rotational speed of the motor is decreased and the agitator is alternately rotated in normal and reverse directions with the rotatable tub being stopped by a braking force. In execution of a dehydration operation, the rotational speed of the brushless motor is not decreased with the rotatable tub being released from the braked state and both the rotatable tub and the agitator are rotated at high speeds.
To drive the rotatable tub and the agitator as described above, a belt transmission mechanism, a clutch mechanism, a gear reduction mechanism including planetary gears, etc. are provided in a rotation transmission path from the motor to the rotatable tub and the agitator. However, these driving mechanisms increase the weight and the height of the washing machine. Furthermore, the gear reduction mechanism produces loud noise during operation.
Hence, what is needed is an improved drive control that eliminates the need for a belt transmission mechanism and a gear reduction mechanism to reduce the weight and height of the washing machine, and eliminate the noise produced by the gears. In addition, the electric motor used with the drive control needs to produce high torque and its rotational speed needs to be variable in a broad range of speed--from low to high. The torque variations, however, results in vibration of the motor, which produces noise. Accordingly, the noise emanating from the motor should be better controlled.